# 40005: Layer's dataset is using an unknown coordinate system

A coordinate system is required for your layer's dataset when creating a package.

## Solutions

- Define the coordinate system of the layer's dataset.
- Remove the layer from your package.

## More information

Coordinate systems provide a mechanism for describing geographic data on a 2D and 3D surface. It is considered a best practice to have a coordinate system defined for your map or layer so that it can be correctly represented and integrated with other layers of a map.

**Changing the data frame's coordinate system**

- Right-click the data frame for which you want to determine the coordinate system.
- Click Properties.
- Click the Coordinate System tab. The details of the current data frame coordinate system are shown in the dialog box.
- For more information, see Specifying a coordinate system.

**Changing the coordinate system of a map layer**

You must define the coordinate system of the data source used for the map layer. See the Define Projection geoprocessing tool for more information.

8/20/2010